1. Field of the Invention
The present invention relates to a suction apparatus of a multi-cylinder internal combustion engine, particularly to such a suction apparatus having a plurality of independent suction passages of equal length.
2. Description of the Related Art
In a multi-cylinder internal combustion engine for a vehicle, it has been practiced generally to change passage length or volume of a suction pipe in accordance with rotative speed of the internal combustion engine for utilizing inertia supercharging effect and resonance (pulsation) supercharging effect of suction air in order to maintain high volumetric efficiency over a wide rotative speed region from a low rotative speed region to a high rotative speed region.
Japanese Laid-Open Patent Publication No. 7-91263 discloses such a multi-cylinder internal combustion engine which has a resonance vessel attached to a suction passage to improve resonance supercharging effect of suction air particularly in a low speed region.
This engine is longitudinally mounted on a vehicle, namely mounted on a vehicle with a crankshaft directed lengthwise of the vehicle, and has a suction apparatus comprising a plurality of independent suction passages of equal length. Each of the independent suction passages has a downstream end communicating with a corresponding cylinder and an upper stream end communicating with a suction gathering chamber.
Each independent suction passage has an upper stream portion arranged along a row of cylinders (in lengthwise direction of the vehicle) at one side of the engine with respect to the row of cylinders, a downstream portion extending toward the engine and a curved portion formed between the upper stream portion and the downstream portion so as to change direction of the passage.
The curved portions of the respective suction passages are disposed so that a line connecting centers of the curved portions is inclined with respect to the row of cylinders so as to be distant from the eigne at a side of the gathering chamber. And on outside of the curved portions is disposed a resonance vessel communicating with the gathering chamber along the above-mentioned center connecting line.
A suction pipe forming the independent suction passage is divided into two pipe sections at the curved portion and both the pipe sections are connected with each other by means of a flange. The resonance vessel is fixed to the flange.
Japanese Laid-Open Patent Publication No. 2-199266 discloses a suction apparatus of a multi-cylinder internal combustion engine laterally mounted on a vehicle which comprises a surge tank (gathering section of a plurality of independent suction passages), a plurality of curved independent suction passages extending from the surge tank to communicate with respective cylinders, a resonance chamber provided inside of curved sections of the suction passages between the surge tank and the suction passages, and a communication passage connecting the surge tank and the resonance chamber.
The above communication passage is formed snaking along a side surface of the independent suction passages and an end of the communication passage facing toward the surge tank is provided with a communication opening which is formed in the neighborhood of an end surface of the surge tank opposite to another end surface provided with a throttle body.
The suction apparatus is divided into an upper half body and a lower half body by a common partition surface halving the independent suction passages, the resonance chamber and the communication passage respectively.
In the suction apparatus of the japanese Publication No. 7-91263, since the resonance vessel is arranged on one side of the suction manifold along the independent suction passages, the resonance vessel protrudes in a direction perpendicular to the row of cylinders to obstruct miniaturization of the suction apparatus, and a connecting member such as a tube is necessary for connecting the resonance vessel to the gathering section of the independent suction passages so that the number of parts is increased and assembling works are necessary.
Since the connecting pipe for connecting the resonance vessel to the gathering section of the independent suction passages is long, though suction characteristic in a low rotative speed region can be improved, improvement of suction characteristic in middle and high rotative speed region by utilizing resonance supercharging effect is difficult because enlargement of diameter of the connecting pipe is limited. If the diameter of the connecting pipe is merely enlarged to a possible extent, the resonance chamber itself may serve as a volume of the gathering section of the independent suction passage. In this case, the resonance supercharging effect by utilizing the resonance chamber can not be expected.
Further, since the resonance vessel is fixedly connected to the flanges of the independent suction passages, vibration of the engine main body is directly transmitted to the resonance vessel and the resonance vessel generates secondary radiating sound so that deterioration of acoustic commercial quality of the engine is feared and stabilization of suction characteristic in resonance supercharging utilizing the resonance chamber is liable to be injured.
With respect to the suction manifold itself, since a mass vibrating with the same phase is increased, the vibration is accelerated and durability of suction control parts such as a throttle body connected to the suction manifold is liable to be deteriorated.
The gathering section of the independent suction passages is disposed at a position where undergoes heat from a front part of the engine room after passing through a radiator and heat from an upper part of the engine room, therefore, it is feared that lowering of engine out put and deterioration of engine starting nature are caused.
On the one hand, the suction apparatus of the latter Japanese publication No. 2-199266 has problems as follows.
An communication opening of the communication passage facing the surge tank is formed on a bottom surface of the surge tank at a position near an end surface opposite to an end surface with the throttle body fitted, therefore, suction air pressure wave turned at the suction gathering section including the resonance chamber and the surge tank advances against suction air entering passing through the throttle body undergoing an influence of the suction air, as the result, the suction air pressure wave is damped in the surge tank and the independent suction passages, so that resonance supercharging effect of the suction air can not be exhibited enough.
Also in this suction apparatus, more than half of the independent suction passages and the surge tank which is a gathering section of the independent suction passages is positioned at a place where undergoes heat from a front part of the engine room after passing through a radiator and heat from an upper part of the engine room, therefore, it is feared still that lowering of engine out put and deterioration of engine starting nature are caused.
The present invention is accomplished in order to overcome the above difficulties, and an object of the invention is to provide a suction apparatus of a multi-cylinder internal combustion engine having a plurality of independent suction passages and a resonance vessel in which the suction apparatus can be made compact, vibration of attachment construction of the resonance vessel can be prevented, suction characteristic (volumetric efficiency or charging efficiency) particularly in middle and high rotative speed region can be improved, and lowering of engine out put can be prevented by sheltering suction system from heat in the engine room.